1. Field of the Invention
The present invention relates to a control device for a vehicular drive system, and more particularly to a vehicular drive system which includes a differential mechanism operable to perform a differential function, and a transmission constituting a part of a power transmitting path between the differential mechanism and drive wheels, and which is improved in the durability of coupling devices provided to switch a power transmitting path between an engine and the drive wheels, between a power-cutoff state and a power-transmitting state.
2. Discussion of Related Art
There is known a vehicular drive system including a differential mechanism operable to mechanically synthesize forces and distribute a force, and an electric motor operatively connected to the differential mechanism. Examples of this type of vehicular drive system include a drive system for a hybrid vehicle as disclosed in Patent Document 1. In this hybrid vehicle drive systems, the differential mechanism is constituted by a planetary gear set, and a so-called “electric torque converter” is provided to transmit a drive force from an engine to drive wheels, according to a reaction torque of an electric motor. The vehicular drive system of the Patent Document 1 further includes a step-variable automatic transmission disposed in a power transmitting path between the planetary gear set and the drive wheels. The power transmitting path between the engine and the drive wheels is switched between a power-cutoff state and a power-transmitting state, by controlling releasing and engaging actions of clutches incorporated in the step-variable automatic transmission. The vehicle disclosed in the Patent Document 1 is provided with a manually operable shifting device operable to switch the power transmitting path between a non-drive position for establishing the power-cutoff state, and a drive position for establishing the power-transmitting state.                [Patent Document 1] JP-9-308010A        [Patent Document 2] JP-1-113531A        [Patent Document 3] JP-1-76336A        
When the above-described shifting device is manually operated from the non-drive position to the drive position, an output torque of the engine (hereinafter referred to as “engine torque”) is transmitted to the drive wheels through the step-variable automatic transmission.
However, the manual operation from the non-drive position to the drive position has a risk of deterioration of durability of the coupling devices provided for switching of the power transmitting path between the power-cutoff state and the power-transmitting state. The risk of deterioration increases with an increase of the engine torque to be transmitted.